Cigarettes are conventionally made by wrapping a column of tobacco in a white wrapping paper. Cigarettes also usually include a filter joined to one end of the tobacco column by a tipping paper. Wrapping papers and tipping papers are typically made from flax or other cellulosic fibers and contain a filler, such as calcium carbonate.
Besides being used to hold the cigarette together and to provide the cigarette with an aesthetic appearance, cigarette wrapping papers also contribute to or control many physical properties and characteristics of the cigarette. For instance, cigarette wrapping paper can be used to control the rate in which the cigarette burns, the number of puffs per cigarette, and the total tar delivery per puff. Cigarette paper can also be used to limit the amount of smoke that emanates from the lit end of the cigarette when it is left burning. Further, cigarette paper is even used to reduce the tendency of cigarettes to ignite surfaces which come in contact with the cigarette and to cause the cigarette to self-extinguish when left unattended.
Perhaps the most important property of cigarette wrapping paper that is used to control the above-described characteristics of a cigarette is permeability. By increasing or decreasing the permeability of a wrapping paper, many changes occur in a cigarette made from the paper, including most importantly the overall taste of the cigarette.
In the past, many of those skilled in the art have devised various methods for controlling and adjusting the permeability of cigarette wrapping paper. For instance, one method of altering the permeability of wrapping paper is to vary the fiber furnish that is used to make the paper.
Another method of controlling permeability of a wrapping paper is to either increase or decrease the refining of the fiber furnish. Generally speaking, refining the fiber furnish to a greater extent causes a reduction in permeability. More particularly, refining the cellulosic material that is used to make the paper down into smaller sizes creates more surface area, which reduces permeability and leads to better formation.
A third way in which the permeability of cigarette paper is controlled is to change the amount of filler added to the paper. Increasing or decreasing the filler loading of the paper causes an increase or decrease in permeability respectively. As more filler is added to the paper, the filler tends to interfere with the hydrogen bonding between fibers creating the increase in permeability.
Of the above three methods, increasing or decreasing the filler level is perhaps the simplest method for adjusting permeability. Unfortunately, however, altering filler levels in cigarette paper also affects the burn rate of the cigarette independently of permeability. As burn rate changes, so does puff count and total tar delivery.
Other problems are also experienced when filler levels are altered. For instance, as filler content is increased, the strength of the paper is compromised. Conversely, when not enough filler is incorporated into the paper, the opacity of the paper significantly decreases, adversely affecting the appearance of the cigarette. Therefore, there is increasing pressure to keep filler levels in cigarette paper constant or at least within a preset range, thereby leaving the amount of refining and the selection of furnish as the only tools for permeability adjustments.
Thus, a need exists for a simple method of adjusting the permeability of a cigarette paper without adversely affecting various characteristics of the paper and without having to significantly alter the amount of filler contained within the paper. A need also exists for a method of controlling the permeability of cigarette paper that can be used in conjunction with refining adjustments and furnish selection. Further, there is also a need for a system that will automatically maintain or adjust the permeability of a paper as the paper is being made.